1. Field of the Invention
The present invention relates to a data recording clock signal generator that generates a recording clock signal used for recording data on a recording medium, such as an optical disk or hard disk, in a data recording device.
2. Description of the Related Art
Known recording media having a data recording track wobbled by a wobble signal having predetermined frequency components include optical disks, such as CD-R, CD-RW, DVD-R, and DVD-RAM. Japanese Laid-Open Patent Application Nos. 10-293926 and 11-66563 each disclose a data recording clock signal generator that generates a recording clock signal synchronous with a wobble signal of an optical disk.
A rewritable optical disk has a drawback that repeated recording on the same spot makes the recording mark and its vicinity deteriorate due to thermal stress, and precise mark recording cannot be performed on that spot when a different signal is recorded. To avoid such a situation, Japanese Patent Publication No. 8-10489 and Japanese Laid-Open Patent Application No. 10-3667 disclose an optical disk recording method and an optical disk device in which the recording starting point is made variable so that the use of one particular spot is prevented, and the disk material can be used a greater number of times.
Also, Japanese Laid-Open Patent Application No. 10-69646 discloses a data recording clock signal generator that generates a recording clock signal synchronous with a wobble signal on which address information and other signals are phase-modulated and superimposed.
FIG. 1 is a block diagram showing an example structure of a conventional optical disk driving device.
An optical disk 1 has a data recording track wobbled by a wobble signal having prescribed frequency components.
FIG. 2 shows the structure of wobbled data recording track on the optical disk 1.
A land portion indicating the locations of the track is wobbled in accordance with address information, and the address information and a synchronizing signal are modulated and superimposed on the wobble signal.
In the conventional optical disk driving device shown in FIG. 1, an optical pickup (PU) 2 emits a laser beam onto a data recording track on the optical disk 1. The laser beam reflected from the track on the optical disk 1 is returned to the optical pickup 2, and is converted into an electric signal by a detector in the optical pickup 2.
An amplifier 3 amplifies the electric signal detected by the optical pickup 2 and outputs a reproducing signal RF corresponding to data recorded on the optical disk 1 and a wobble signal WBL corresponding to the wobble of the track. The reproducing signal RF is detected when the data is reproduced, and the wobble signal WBL is detected when the data is either recorded or reproduced.
A recording clock generator circuit 4 generates a recording clock signal WCLK which is synchronous with the wobble signal WBL.
FIG. 3 is a block diagram showing an example structure of the conventional recording clock generator circuit shown in FIG. 1.
The recording clock generator circuit 4 is constituted by a PLL (Phase-Locked Loop) circuit.
A phase comparator 41 compares the phase of a wobble signal WBL with the phase of a signal obtained by dividing the frequency of a recording clock signal WCLK at a predetermined frequency dividing rate by a frequency divider 45.
The output of the phase comparator 41 is converted into a voltage signal by a charge pump 42, smoothed by a filter 43, and then inputted into a VCO (Voltage Controlled Oscillator).
The frequency of the output clock of the VCO, which is the recording clock signal WCLK, is controlled by an input voltage. As a result, the phase of the recording clock signal WCLK becomes synchronous with the wobble signal WBL.
Now referring back to FIG. 1, a synchronous detector circuit 5 and an address decoder 6 of the conventional optical disk driving device detect the synchronizing signal and the address information, respectively, superimposed on the wobble signal.
When data recording is carried out, a data encoder 8 synchronizes with the recording clock signal WCLK to perform a predetermined modulation process on the recording data.
An LD driver 9 modulates the strength of laser beams emitted from the optical pickup 2 in accordance with the modulated recording data. As a result, the data recording can be carried out in synchronization with the wobble signal of the data recording track.
According to the technique disclosed in Japanese Patent Publication NO. 8-10489, however, a plurality of analog delay circuits are required for obtaining random recording starting points, resulting in higher production costs.
In the conventional recording clock generating circuit, the phase of the recording clock signal WCLK is constantly synchronous with the wobble signal WBL, as long as the wobble signal is properly detected. However, minor defects might exist on the optical disk, or dirt or dust might stick to the surface of the optical disk. At the locations corresponding to those defects or the areas to which dirt or dust sticks, the wobble signal is lost, and cannot be detected properly.
In the recording clock generating circuit constituted by the conventional PLL circuit, a small loss of the wobble signal can be ignored, and the phase synchronization between the wobble signal and the recording clock signal can be maintained thanks to a so-called flywheel effect of the PLL. However, if there is a large loss of the wobble signal, a phase shift is caused between the wobble signal and the recording clock signal. After the loss, the phase of the recording clock signal is shifted by a whole number of cycles of the wobble signal. This situation is called a bit slip.
When there is a bit slip in the recording clock signal, the phase difference between the wobble signal and the recording clock signal cannot be compensated, and data recording is performed at locations deviated from predetermined locations. If new data recording is started after data recording is completed in one sector, with a bit slip remaining in the recording clock signal, data overlapping or unnecessary blank is caused at the connecting portions between the previous recording data and the new recording data. In such a situation, the data recorded in the vicinity of the connecting portion is not properly reproduced.
In the case where address information and other signals are phase-modulated and then superimposed on a wobble signal on an optical disk (as disclosed in Japanese Laid-Open Patent Application No. 10-69646, for instance), a drastic change occurs in the phase of the wobble signal due to the phase modulation, and a phase shift is caused between the wobble signal and the recording clock signal.